Blender Git Loki

Modification of node groups by adding/removing nodes is not possible yet. This patch extends the 'Make Group' operator and adds a new 'Separate' operator to add such functionality.

1) For inserting into existing groups:
The 'Make Group from selected' (CTRL+g) operator shows a selection popup (like the object parenting operator), with options depending on the type of the active node (last selected):
* "New" -> regular operator, creates new group type with all selected nodes inside.
* "Insert" (only if active node is a group) -> adds all other selected nodes into the group.

Currently still prohibits groups inside groups in general, though would be technically possible as long as no actual recursion occurs (group containing itself).

2) For extracting from an existing group:
New 'Separate from group' operator (p), works similar to separating vertices/edges/faces from mesh. Two modes:
* "Copy" makes a copy of the nodes in the parent tree, but keeps the original group intact.
* "Move" removes selected nodes from the node group and adds them to the parent tree